Electro-optic materials are those whose optical properties change in accordance with the strength of an electric field established within them. These materials make possible an electrically controlled electro-optic modulator for use in a light valve array.
One well known form of electro-optic modulators are total internal reflection (TIR) modulators which can be employed in laser-based imaging systems for example. FIGS. 1A and 1B schematically show plan and side views of a conventional TIR modulator 10 comprising a member 12 which includes an electro-optic material and a plurality of electrodes 15 and 16 arranged in an interdigitated relationship on a surface 18 of member 12. Surfaces 20 and 22 are arranged to cause input radiation 25 to refract and undergo total internal reflection at surface 18.
In this typical conventional configuration, various electrodes 15 and 16 are grouped into electrode groups S1, S2, S3, S4 . . . Sn which are collectively referred to as electrode groups S. Each of the electrodes 15 in each of the groups are driven with a corresponding one of individually addressable voltages sources V1, V2, V3, V4 . . . Vn which are operated in accordance with various image data signals. To simplify interconnect and driver requirements, all electrodes 16 are interconnected to a common source (e.g. a ground potential). In this case, electrodes 16 are coupled in a serpentine fashion among all the electrode groups S.
Upon the application of a suitable voltage by one of the voltage sources V1, V2, V3, V4 . . . Vn to an associated one of the electrode groups S1, S2, S3, S4 . . . Sn, an electric field is established in a portion of the of the electro-optic material referred to as a pixel region 11 (i.e. shown in broken lines). In this regard, an electrode group S is associated with each pixel region 11. FIG. 1B shows that each pixel region 11 includes a portion of surface 18 that is impinged by radiation 25.
The application of the voltage alters the refractive index of the electro-optic material, thereby changing a birefringent state of the pixel region 11. Under the application the corresponding drive voltage, the arrangement of electrodes 15 and 16 in each of the electrode groups S1, S2, S3, S4 . . . Sn causes each of the electrode groups to behave in a manner similar to a diffraction grating. A birefringent state of each of the pixel regions 11 can therefore be changed in accordance with the selective application of various voltages by an associated one of voltage sources V1, V2, V3, V4 . . . Vn. For example, in this case when no voltage is applied to a particular electrode group S, an associated pixel region 11 assumes a first birefringent state in which output radiation 27 is emitted from surface 22 and is directed by one or more lenses (not shown) towards a surface of a recording media (also not shown) to form an image pixel thereon. In the case when a suitable voltage is applied to a particular electrode group S, the associated pixel region 11 assumes a second birefringent state in which output radiation 27 is emitted from surface 22 in a diffracted form which can be blocked by an obstruction such as an aperture (also not shown) to not form an image pixel.
Various image features are formed on a recording media by combining image pixels into arrangements representative of the image features. It is a common desire to form high quality images with reduced levels of artifacts. In particular, the visual quality of the formed image features is typically dependant on the visual characteristics of the formed image pixels themselves. For example, one important characteristic is the contrast between an image feature and surrounding regions of the recording media. Poor contrast can lead to the formation of various image features whose edges lack sharpness or are otherwise poorly defined. Another important characteristic is the accurate placement of the image pixels on the recording media.
The previously described conventional method of driving the arrangement of electrodes 15 and 16 can lead to various problems which can adversely impact a desired visual characteristic of the final image. For example, the sharpness of feature edges can suffer or an undesired deflection of output radiation 27 can arise. FIG. 1C schematically shows a subset of electrode groups S1, S2, S3, and S4 driven with various voltage levels by their corresponding voltage sources as follows: (V1:V); (V2:V); (V3:0); and (V4:V). Voltage level “V” corresponds to a drive voltage level selected to cause substantial diffraction to be created within a pixel region 11 whereas voltage level “0” corresponds to a voltage level (i.e. a ground potential in this case) selected to not cause substantial diffraction to be created within a pixel region 11. When a pixel region 11 is made non-diffracting (e.g. the pixel region 11 corresponding to electrode group S3), the average electric potential of the electrodes 15 and 16 of the pixel region is null. However, when a pixel region 11 is made diffracting (e.g. the pixel regions 11 corresponding to electrode groups S1, S2 and S4) the average electric potential of the electrodes 15 and 16 of the pixel region 11 is approximately V/2. This creates an electric potential difference of V/2 between the average voltages of non-diffracting and diffracting regions of TIR modulator 10. This can give rise to long-range electric fields that deflect radiation that is propagated within the electro-optic material to produce a beam steering effect. Although the long-range fields can be relatively weak, they typically interact with the radiation over a longer path length than the shorter range diffraction grating fields. TIR modulator 10 is an example of an “unbalanced” TIR modulator.
One possible consequence of this deflection is that image pixels formed on the recording media can be shifted and a placement error arises. The degree of the placement error can vary in accordance with the image data which controls the selective application of the drive voltages. Another possible consequence can include an increase in the diffraction broadening of an image pixel since the output radiation 27 is deflected to one side in the pupil of the imaging system, thereby reducing the effective aperture of the system. Other possible consequences can include an increased sensitivity to aberrations in the imaging system.
Commonly-assigned U.S. Pat. No. 7,656,571 B1 (Reynolds) describes a total internal light modulator in which potential differences between diffracting and non-diffracting regions of the modulator are balanced. FIGS. 2A and 2B schematically show corresponding plan and side views of a TIR modulator 100 similar to a modulator described in U.S. Pat. No. 7,656,571. TIR modulator 100 includes a member 112 comprising an electro-optic material 113. A plurality of electrodes 115 and 116 are arranged on a surface 118 of member 112. Member 112 includes surfaces 120 and 122 which are arranged to cause radiation 125 to refract and undergo total internal reflection at surface 118.
As shown in FIG. 2A, each of the electrodes 115 and 116 is elongate in form and extends along a direction that is substantially parallel to an overall direction of travel 126 of radiation 125. As shown in FIG. 2A, electrodes 115 are arranged in a plurality of first sets while electrodes 116 are arranged in a plurality of second sets. Each set of electrodes 115 is electrically driven by a corresponding one of individually controllable first voltage sources: VJ1, VJ2, VJ3, VJ4 . . . VJn (i.e. collectively referred to as first voltage sources VJ) via a corresponding one of a plurality of electrical conductors 128A arranged on surface 118. Each set of electrodes 116 is electrically driven by a corresponding one of individually controllable second voltage sources: VK1, VK2, VK3, VK4 . . . VKn (i.e. collectively referred to as second voltage sources VK) via a corresponding one of a plurality of electrical conductors 128B arranged on surface 118. In this case, each of the first voltage sources VJ is coupled to an associated one of the electrical conductors 128A at an interconnect element 130A provided on surface 118. In this case, each of the second voltage sources VK is coupled to an associated one of the electrical conductors 128B at an interconnect element 130B provided on surface 118. Each of the electrical conductors 128A and 128B acts as feed line between associated interconnect elements and electrode sets. FIGS. 2A and 2B show that each of the electrical conductors 128A extends over a non-pixel region 132A and that each of the electrical conductors 128B extends over a second non-pixel region 132B. As shown in FIG. 2B, neither of non-pixel regions 132A and 132B includes a portion of surface 118 that is impinged by radiation 125. Pixel regions 110 and non-pixel regions 132A and 132B are each shown in broken lines in FIG. 2A.
Each set of electrodes 115 is arranged with a set of electrodes 116 such that their respective electrodes are interdigitated with respect to one another within an associated one of electrode groups T1, T2, T3, T4 . . . Tn (i.e. collectively referred to as electrode groups T). As shown in FIG. 2A and 2B each electrode group T is associated with one of a plurality of pixel regions 110 that are directly impinged by radiation 125.
FIG. 2C schematically shows a subset of the electrode groups T (i.e. electrode groups T1, T2, T3, and T4) of light modulator 100 driven by their corresponding voltage sources VJ and VK to establish various electric potentials on each of the sets of electrodes 115 and 116 associated with each of the electrode groups T. In particular, FIG. 2C shows that electrode groups T1, T2, T3, and T4 are driven by corresponding voltage sources VJ and VK as follows: (VJ1:+V/2, VK1:−V/2), (VJ2:+V/2, VK2:−V/2), (VJ3:0, VK1:0), and (VJ4:+V/2, VK4:−V/2). The voltages combinations of “+V/2” and “−V/2” correspond to drive voltages that are applied to an electrode group T to cause substantial diffraction within a pixel region 110 associated with the electrode group T. In this regard, a difference of V Volts between these two potentials is sufficient to cause the diffraction. The voltage combinations of “0” and “0” correspond to drive voltages that are applied to an electrode group T to not cause substantial diffraction within a pixel region 110 associated with the electrode group T. In this regard a difference of 0 Volts is insufficient to cause diffraction.
In this case, TIR modulator 100 is driven such that the averages of the voltage combinations used to create each of the different birefringent states in a pixel region 110 are substantially equal to one another. That is, the average voltages used to create a substantially non-diffracting state in a pixel region 110 (i.e. the average of 0 Volts and 0 Volts) substantially equals an average of the voltages used to create a substantially diffracting state in a pixel region 110 (i.e. the average of +V/2 Volts and −V/2 Volts). FIG. 2C schematically shows the average electric potentials imposed on the electrodes 115 and 116 of electrode groups T1, T2, T3, and T4 in this case. Unlike the aforementioned TIR modulator 10 in which a variance of V/2 Volts existed between the average electrical potentials of the non-diffracting and diffracting pixel regions 11 of TIR modulator 10, such variances are reduced in the TIR modulator 100. TIR modulator 100 is an example of a “balanced” TIR modulator.
It has been noted by the present inventors that other electrically conductive members (i.e. other than the interdigitated electrodes) can also generate electric field within an elector-optic material of a light modulator. In case of the TIR modulator 100, the present inventors have noted that a set of electrical conductors (e.g. the set of electrical conductors 128A or the set of electrical conductors 128B) can lead to the creation of an electric field. It has been noted that the electric field created by set of electrical conductors 128A or 128B typically penetrates more deeply into electro-optic material 113 than an electric field created by the electrodes in an electrode group T. This effect is simulated in FIG. 2B where an electric field 136 is generated by various electrical conductors 128A and an electric field 138 is generated by various electrical conductors 128B. Each of the generated electric fields 136 and 138 penetrate member 112 in the vicinity of non-pixel regions 132A and 132B, respectively. Although the electric fields 136 and 138 are associated with non-pixel regions 132A and 132B that include portions of surface 118 that are not directly impinged by radiation 125, electric fields 136 and 138 penetrate sufficiently within the electro-optic material 113 to interact with radiation 125. Electric fields 136 and 138 can lead to various problems including undesired beam steering of the radiation 125 that is outputted from TIR modulator 100.
There is a need for improved TIR modulators that can further reduce beam steering effects.
There is a need for improved balanced and unbalanced TIR modulators that can further reduce beam steering effects.